Shaped yarns for use in papermaking fabrics

ABSTRACT

A papermaking fabric with increased stability is provided, due to the use of beam construction yarns which resist lateral, vertical and torsional deflection as well as compression when interwoven. The yarns are generally non-circular in cross-section and are preferably I-beam, H-beam, box-beam or a hybrid construction. Each type has certain advantages, with the hybrid construction being capable of multiple combined advantages.

BACKGROUND

The present invention is directed to papermaking fabrics having shapedyarns, and more particularly to papermaking fabrics made with structuralyarns shaped for enhanced lateral, vertical and torsional stability.

Papermaking fabrics are subjected to harsh environments through everystage of the papermaking process. Forming fabrics are exposed to highmoisture and caustic chemicals in the forming section as the paper webis formed on the fabric surface. Press fabrics are also exposed to highmoisture and high contact pressure in the nip between press rolls in thepress section where the paper web is de-watered. Dryer fabrics aresubject to both high heat and humidity in the dryer section as the paperweb is dried to form the final paper product. All of these papermakingfabrics must maintain dimensional and structural stability throughoutthe fabric life in order to support the paper web. Movement through thevarious machine rolls causes a great potential for lateral (Y), vertical(Z) or torsional (rotation) displacement of circular yams typically usedin papermaking fabrics.

Traditionally, papermaking fabrics were woven with yarns having circularcross-sections. Their uniform shape negated worries about rotationaldistortion-except for twist problems. These yarns, however, were subjectto lateral displacement where one yarn slides toward another yarn,creating an open area and a bunched area, rather than uniform contactand open areas. The fabric therefore suffered from lack of control ofcontact surface area and permeability.

To combat lateral displacement of structural yarns, shaped yarns (suchas I, U or X-shaped yarns) have been used to cradle structural yarns tolessen the amount of displacement relative to one another in multilayerfabrics. Yarns having X or Y shapes or otherwise having flexible legportions have been used in the weft position to enhance permeabilitycontrol and for stabilization against distortion. Shaped yarns have alsobeen used as stuffer yams to fill voids in spiral fabrics to reduce thefabric permeability.

A common theme with the prior known shaped yarns is that they deformduring the weaving process to lock themselves into position. In thedeformed shape, these yarns are more stable and also act to stabilizethe cross-direction yarns. This is seen in both hollow and shaped yarns.Many of these shaped yarns (X, I, H, Y) as well as hollow yamsaccomplish goals of increased stability, reduced displacement andpermeability control. However, they do not directly address lateral,vertical and torsional displacement in the structural yarns of apapermaking fabric.

It would be desirable to provide a papermaking fabric which willwithstand the ravages of a papermaking machine and resist lateral,vertical and torsional displacement.

SUMMARY

Generally, the present invention is a papermaking fabric which hasincreased stability due to the use of beam construction yarns whichresist lateral, vertical and torsional deflection as well ascompression, when interwoven as structural yams. The yarns are generallynon-circular in cross-section and are preferably I-beam, H-beam,box-beam, or a hybrid construction. Each type has certain advantages anddisadvantages with the hybrid construction being capable of multiplecombined advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe preferred embodiments of the invention, will be better understoodwhen read in conjunction with the appended drawings. For the purpose ofillustrating the invention, there is shown in the drawings embodimentswhich are presently preferred. However, it will be understood by thoseskilled in the art from the present disclosure that the invention is notlimited to the precise arrangements shown. In the drawings:

FIG. 1 is a cross-sectional view of a portion of a papermaking fabrichaving I-beam cross-machine direction yarns and H-beam, machinedirection yarns.

FIG. 2 is a cross-section of a portion of a papermaking fabric inaccordance with a second embodiment of the present invention havingI-beam cross-machine direction yarns.

FIG. 3 is a cross-section of a portion of a papermaking fabric havingbox-beam machine direction and cross-machine direction yarns.

FIG. 4 is a cross-section of a portion of a papermaking fabric inaccordance with a fourth embodiment of the present invention havinghybrid box-beam cross-machine direction yarns.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Certain terminology is used in the following description for convenienceonly and is not limiting: “right,” “left,” “lower” and “upper” designatedirections in the drawings to which reference is being made. Theterminology includes the words specifically noted above as well asderivatives thereof and words of similar import. Additionally, the words“a,” “and” and “one” are understood to mean one or more of thedesignated items unless specifically noted.

Referring now to FIG. 1, a portion of a papermaking fabric 10 is shown.The papermaking fabric includes machine direction yarns 12 andcross-machine direction yarns 14. The machine direction yarns 12 have anH-shaped cross-section to provide a high contact area and goodZ-direction (vertical) stiffness. The machine direction yarns also haveexceptional Y-direction (lateral) stiffness, due to the width of theupper and lower flanges.

Preferably, the cross-machine direction yarns 14 have an I-beam shapedcross-section, having extremely high bending stiffness in theZ-direction. I-beams also provide moderate Y-direction and torsionresistance.

The machine direction and cross-machine direction yarns 12 and 14 arepreferably extruded monofilament yarns extruded in the known manner, aswill be understood as those skilled in the art. The yarns may be drawnand quenched, depending upon the properties desired. The fabric 10 isshown as having a plain weave. However, it will be recognized by thoseskilled in the art for under present disclosure that the weave can beany desired weave, such as a crows foot or sateen, if desired.

Referring now to FIG. 2, a portion of a second embodiment of apapermaking fabric 20 is shown. The fabric 20 includes machine directionyarns 22 and cross-machine direction yarns 24. The cross-machinedirection yarns 24 are preferably I-beam shaped yarns having the centralweb oriented generally horizontally. This provides a fabric withincreased strength, stiffness and a lower caliper. The machine directionyarns 22 are shown as monofilaments having a circular cross-section.However, it will be recognized by those skilled in the art from thepresent disclosure that the machine direction yarns 22 could have anyother desired cross-sectional shape, depending upon the propertiesdesired. Preferably the machine direction and cross-machine directionyarns 22, 24 are extruded in the known manner.

Referring now to FIG. 3, a portion of a third embodiment of apapermaking fabric 30 is shown. The fabric 30 includes machine directionyarns 32 and cross-machine direction yarns 34. Preferably, both themachine and cross-machine direction yarns 32 and 34 have a generallyboxed-shaped cross-section with a hollow center. This constructionprovides good contact area and stiffness in the lateral and verticaldirections to provide a high stability, high contact fabric having a lowmass, due to the use of hollow yarns 32, 34. The box-beam configurationalso provides exceptional torsion resistance in order to maintainexcellent fabric dimensional stability. While the portion of fabricshown has a two-over, two-under weave, it will be recognized by thoseskilled in the art from under present disclosure that other weavepatterns can be used, if desired.

Referring now to FIG. 4, a fourth embodiment of a fabric 40 is shown.The fabric 40 has machine direction yarns 42 and cross-machine directionyarns 44. The machine direction yams 42 are illustrated as monofilamentshaving a circular cross-section. The cross-machine direction yarns arepreferably a hybrid cross-section, combining the box-beam and the H-beamto provide a high contact area, good Z-direction (vertical) andY-direction (lateral) stiffness, as well as exceptional torsionresistance. Preferably the machine direction and cross-machine directionyarns are extruded monofilaments which are extruded in the known manner.The materials used for the yarns can be PET, PA, polyethylene or anyother desired material, depending upon the properties required.

It will be recognized by those skilled in the art from the presentdisclosure that the fabric embodiments 10, 20, 30, and 40, as shownabove, are merely exemplary and that other configurations could be usedto provide fabrics with increased stability due to the use of interwovenstructural yarns which preferably have I-beam, H-beam, box-beam and/orhybrid cross-sections. It will be similarly recognized that the wovenfabrics 10, 20, 30 and 40 can be used as forming fabrics or as basematerials for press or dryer fabrics, with batting being needled oradhered to the base fabric, if desired.

It will therefore be understood by those skilled in the art from thepresent disclosure that changes could be made to the preferredembodiments described above without departing from the broad inventiveconcept thereof. Accordingly, the present invention is not limited tothe particular embodiments disclosed, and is intended to covermodifications within the spirit and scope of the present invention.

What is claimed is:
 1. Papermaking fabric comprising interwoven machine direction and cross-machine direction yarns, at least one of the machine direction and cross-machine direction yarns comprising a structural yarn having a non-circular cross-section selected from one of an I-beam, an H-beam, a box-beam and a hybrid construction. rn 